The present invention relates to a process for preparing a hydrogenated petroleum resin, and more particularly to a process for hydrogenating a petroleum resin in a high efficiency in a shortened reaction time by concurrently passing a hydrogen gas and a molten petroleum resin through a fixed bed of a supported particular metal catalyst.
So-called petroleum resins prepared by polymerizing a thermal cracking product of petroleum naphtha in the presence of a Friedel-Crafts catalyst have been employed mainly as a tackifier for adhesives and a modifier for plastics. Petroleum resins suitable for these purposes are usually those having a softening point of 60.degree. to 140.degree. C. and a molecular weight of 600 to 10,000. In particular, hydrogenated products of such petroleum resins are suitable for these purposes, because they have good weatherability, color, stability and compatibility with rubbers, polyolefins and ethylene-vinyl acetate copolymers. However, these petroleum resins are hard to be hydrogenated as compared with the raw material monomers of the resins. Although the reason has not yet been sufficiently made clear, in general the higher the molecular weight of the petroleum resins, the harder the hydrogenation. Particularly, in case of converting the benzene ring of the petroleum resins into the cyclohexane ring, the hydrogenation reaction is hard to proceed unless the reaction is conducted under severe conditions, namely at high temperature and pressure for a long time in the presence of a large amount of a catalyst.
A nickel catalyst and a platinum catalyst in the form of powder are hitherto known as catalysts for hydrogenation of petroleum resins. Also, a method using a slurry reactor, e.g. a batchwise suspension bed system or a flow type suspension bubble column system, has been generally adopted as a hydrogenation method. In these conventional processes, a powdery catalyst is suspended in a molten petroleum resin, and accordingly a filtration step is essential for separating the catalyst from the hydrogenated petroleum resin after the hydrogenation. However, in case of a petroleum resin having a high softening point, namely having a high melt viscosity, the hydrogenation product must be recovered by once diluting it with an organic solvent such as xylene or toluene, filtering off the catalyst particles and evaporating the organic solvent from the filtrate, because of difficulty in filtration of the product in a molten state or inconvenience in procedure such as requiring a long time for filtration. Accordingly, the steps of the conventional processes are very complicated, and moreover, this results in increase in cost. In particular, in case of using a platinum catalyst which is expensive, the economical loss is large, since the catalyst is not quantitatively recovered. In view of the above-mentioned problems, an industrially, economically advantageous process for the hydrogenation of petroleum resins has been desired.
It is an object of the present invention to provide a process for preparing a hydrogenated petroleum resin which does not require a step for separating a catalyst from the product by filtration as in conventional processes.
A further object of the invention is to provide a continuous process for hydrogenating a petroleum resin utilizing a fixed catalyst bed.
A still further object of the invention is to provide a process for hydrogenating a petroleum resin in a high degree of hydrogenation in a shortened period of time.
These and other objects of the present invention will become apparent from the description hereinafter.